U.S. Pat. No. 6,306,045 discloses a plunging unit which comprises a universal joint with an outer part, an inner part and means for transmitting torque between the outer part and inner part, as well as a journal firmly connected to the inner part and an axially displaceable shaft connected in a rotationally fast way relative to the journal by means of rolling contact members.
For sealing purposes, a convoluted boot is provided which comprises a first collar at the joint end, a second collar at the shaft end and a wall which connects the two collars and comprises folds. The first collar of the convoluted boot is secured by a first attaching part to the outer part of the universal joint, and the second collar of the convoluted boot is secured to the sleeve of the plunging assembly. The convoluted boot prevents dirt from entering the joint and plunging space, and prevents lubricant from leaving the joint and plunging space.
U.S. Pat. No. 6,426,033 discloses a rolling boot made of a thermoplastic elastomer for sealing a universal joint. The rolling boot comprises a first collar with a larger diameter to be secured to an outer joint part of the universal joint and a second collar with a smaller diameter to be secured to a shaft firmly connected to the inner part of the universal joint, as well as a wall in the shape of half a torus for connecting the collars. The rolling boot is produced from a thermoplastic elastomer by injection molding or blow molding.
Using convoluted boots made of a thermoplastic material for sealing the above-mentioned plunging units or plunging joints, especially when such units or joints are used in propeller shafts, is problematical in that the high rotational speeds lead to failure of the convoluted boot. Rolling boots, on the other hand, made of rubber are able to withstand the high rotational speeds, but they are not suitable for compensating for long plunging distances.